Code-domain multiplexing over multicarrier modulation is an efficient multiple-access scheme, such as in multi-carrier-code division multiple access (MC-CDMA), low density signature-orthogonal frequency-division multiplexing (LDS-OFDM), and sparse-code-multiple access-orthogonal frequency-division multiplexing (SCMA-OFDM) systems. A potential application of SCMA-OFDM is grant-less transmission with no or low signaling and control overhead for small packet transmission. A challenge for the uplink (UL) in the grant-less transmission is that a receiver of the UL may have no knowledge of which users and how many of them want to access the network. In this case, there is a possibility of collision between signatures (for users), which results in performance degradation. Another issue is the high complexity of pilot signal detection due to a large number of pilot signals and one-to-many mapping between signatures and pilot signals. There is a need for a mechanism and method for increasing the low density signature space to overcome the issues or challenges above.